1. Technical Field
This disclosure relates to frequency synthesis techniques, and also to a frequency synthesizer with two phase-locked loops and a method for frequency synthesis.
2. Description of Related Art
Due to the advances in wireless communication technologies, portable communication devices are widely used, and the mobile broadband market has been steadily growing. In response to the needs of greater amount of data transmission, mobile communication of new generation focuses on enhancing the transmission speed and bandwidth.
In recent years, 3rd Generation Partnership Project (3GPP) is committed to the development of technology in line with the 4G communication protocols, and has proposed Long-term Evolution-Advanced (LTE-A) Release 10 (R10), which is the first 4G standard recognized by the International Telecommunication Union (ITU). Data transfer rate under high-speed moving environment could reach up to 100 (Mb/s). In LTE-A technology, carrier aggregation is a key technology, which essentially aggregates non-contiguous bands for use at the same time to obtain a greater transmission bandwidth, and enhances the efficient use of bandwidth. For the purpose of carrier aggregation, a transceiver (RF transceiver) in a wireless communication device has to dynamically change the carrier frequency. A wide carrier frequency range means that a frequency synthesizer providing the local frequency must have outputs with very broad bandwidth, but this makes the oscillator design difficult. The complicated bandwidth conditions also pose challenges to the control and frequency resolution of the frequency synthesizer.
Therefore, there is a need in this field for a frequency synthesizer technology that is not only capable of obtaining the target frequency, but also provides I-Q phases in order to comply with the specifications of the frequency output range, while taking into account frequency resolution.